Magnifying the Early Episodes of Star Formation : Super Star Clusters at Cosmological Distances

We study the spectrophotometric properties of a highly magnified (\u3bc 64 40-70) pair of stellar systems identified at Z = 3.2222 behind the Hubble Frontier Field galaxy cluster MACS J0416. Five multiple images (out of six) have been spectroscopically confirmed by means of VLT/MUSE and VLT/X-Shooter observations. Each image includes two faint (mUV 64 30.6), young ( 72100 Myr), low-mass ( 50,000 K) stars within dense stellar clusters, whose dynamical mass is likely dominated by the stellar component. Remarkably, the ultraviolet metal lines are not accompanied by Ly\u3b1 emission (e.g., C IV/Ly\u3b1 > 15), despite the fact that the Ly\u3b1 line flux is expected to be 150 times brighter (inferred from the H\u3b2 flux). A spatially offset, strongly magnified (m > 50) Ly\u3b1 emission with a spatial extent 727.6 kpc2 is instead identified 2 kpc away from the system. The origin of such a faint emission could be the result of fluorescent Ly\u3b1 induced by a transverse leakage of ionizing radiation emerging from the stellar systems and/or may be associated with an underlying and barely detected object (with mUV > 34 de-lensed). This is the first confirmed metal-line emitter at such low-luminosity and redshift without Ly\u3b1 emission-suggesting that, at least in some cases, a non-uniform covering factor of the neutral gas might hamper the Ly\u3b1 detection